Polymethylene thiuram sulfides in vulcanizable compositions



US. Cl. 260-7 9.5

United States Patent Ofice 3,532,678 Patented Oct. 6, 1970 Int. Cl. C08f 27/06 8 Claims ABSTRACT OF THE DISCLOSURE Polymethylene thiuram sulfides of the formula where x is or 6 and y is 1 to 4; are useful as vulcanization accelerators.

BACKGROUND OF THE INVENTION This application is a division of my co-pending application, Ser. No. 518,983, filed Jan. 6, 1966 now Pat. No. 3,468,876.

SUMMARY OF THE INVENTION This invention relates to polymethylene thiuram sulfides. The compounds may be represented by the formula CH2 [wagaflsy CHz S 2 where x is 5 or 6 andy is 1 to 4.

Bis(hexahydrol-azepinylthiocarbonyl) mono and di sulfides have been known since 1941. They were described by Ira Williams and named dihexamethylene thiuram disulfide and dihexamethylene thiuram monosulfide, respectively, US. Pat. 2,236,389. The polymethylene thiuram sulfides accelerate the vulcanization of rubber. It has now been found that the compounds in which x is 5 or 6 impart considerably more processing safety to a vulcanizable rubber composition than the polymethylene thiuram sulfides heretofore known.

PREFERRED EMBODIMENTS The preparation of the compounds is illustrated by the following examples.

Example 1 To a stirred charge containing 67.9 grams (0.6 mole) of heptamethylenimine, 96 grams (0.6 mole) of 25% sodium hydroxide and 500 ml. of water was added dropwise, at 5-15" C., 45.6 grams (0.6 mole) of carbon disulfide and stirring continued at 25-30 C. for an hour. The mixture was then cooled to 0 C. whereupon there was added dropwise at 010 C. in one hour, 75.4 grams (0.33 mole) of ammonium persulfate dissolved in 300 ml. of water. After stirring at 010 C. for 30 minutes, the precipitate was collected by filtration, washed with Water until neutral and air-dried at 45 C. Bis(hexahydro 1(2H) azocinylthiocarbonyl)disulfide was obtained in 98% yield. After recrystallization from ethyl acetate, the cream solid melted at 140141 C. Analysis gave 7.31% nitrogen and 34.11% sulfur compared to 7.44% nitrogen and 34.05% sulfur calculated for C16H28N2S4 Example 2 Following the procedure of Example 1, 76.3 grams (0.6 mole) of octamethylenimine in 1200 m1. of water was substituted for heptamethylenimine. Bis(octahydrolH-azonin-l-ylthiocarbonyl)disulfide was obtained in 98% yield. After recrystallization from an alcohol-benzene mixture, the off-white solid melted at 157158 C. Analysis gave 6.90% nitrogen and 31.88% sulfur compared to 6.92% nitrogen and 31.69% sulfur calculated for C13H32N2S4.

The products of the present invention were tested to determine their effectiveness as rubber vulcanization accelerators in the following tire tread stock:

Parts by weight Stock A B Smoked sheets rubber 100 10) Carbon blaek 50 50 Zinc oxide 5 5 Stearic acid 3 3 Saturated hydrocarbon softener. 3 3 Sulfur 2. 5 2. 5 Bis (hexahyd 1 2H)-azocinylthioearbonyl) disulfide... 0. 5 Bis(oetahydr0- zonin-l-ylthioearbonyl) disulfide 0. 5

The stocks were cured in the usual manner by heating in a press for various periods of time at 144 C. The physical properties of the optimum cures are recorded:

TABLE I Modulus of elasticity in lbs./ Tensile at Ultimate in. at 300% break in, elongation, elongation lbs/in. percent Stock The processing safety of the stocks was evaluated by heating in a Mooney plastometer. The time in minutes required for the plasticity to increase 5 points above the minimum was determined. These values are a measure of processing safety, higher times indicating greater processing safety. The results are recorded below:

TABLE II Mooney scorch Stock: time at 121 C. A 13.6 B 15.7

The Mooney scorch of a similar stock containing as the accelerator 0.5 part of bis(hexahydro-lH-azepin-l-ylthiocarbonyl) disulfide was 11.3 minutes. The stock containing the bis(hexahydro-1H-azepin-l-ylthiocarbonyl) disulfide developed an ultimate tensile strength of 2900 pounds per square inch at optimum cure under the same conditions.

To demonstrate the efficiency of the compounds as vulcanizing agents, tests were carried out employing the compounds on an equimolar basis. Stocks were compounded comprising:

The stocks were vulcanized by heating for different periods of time in the usual manner in a press at 144 C. The modulus and tensile properties of the 40-minute cures and resistance of the unvulcanized compositions to scorch are recorded below:

TABLE Ill Mooney scorch at Example 3 A slurry was prepared by mixing 37.6 grams (0.1 mole) of bis(hexahydro 1(2H) azocinylthiocarbonyl) disulfide prepared as described in Example 1, 7.4 grams (0.11 mole) of potassium cyanide, and 500 ml. of methanol. After heating the slurry at refluxing temperature for 5 hours, it was cooled to 30 C. and 500 ml. of water added. The reaction mixture was then agitated at 2530 C. for 18 hours whereupon the precipitate was collected by filtration, washed with water until the washings were neutral to litmus, and air-dried at 25 30 C. Bis(hexahydro-1(2H) azocinylthiocarbonyl)sulfide was obtained in 75.5% yield as a brown solid. After recrystallization from alcohol, it melted at 9899 C. Analysis gave 8.22% nitrogen and 27.90% sulfur compared to 8.13% nitrogen and 27.9% sulfur calculated for re zs z s- Example 4 Parts by Weight Stock Smoked sheets rubber. Carbon black Zine oxide"... 5 Stearic acid 3 Saturated hydrocarbon softener 3 Suliu 5 r 2. Bis(hcxahydro-1(2l'l)-azocinyltluocarbonyl) sulfide. 0. 5 Bis(octahydro-ll'l-azonin-l-ylthiocarbonyl) sullidc The stocks were cured in the usual manner by heating in a press for various periods of time at 144 C. The physical properties of the optimum cures are recorded:

TABLE IV Modulus Tensile Elongation The processing safety of the stocks was evaluated by heating in a Mooney plastometer. The time in minutes required for the plasticity to increase 5 points above the minimum was determined. The results are recorded below:

4 TABLE V Mooney scorch Stock: at 121 C. F 26.3 G 27.3

The Mooney scorch times of a similar stock containing as accelerator 0.5 part of bis(hexahydro 1H azepin-lylthiocarbonyl)sulfide was 22.7 minutes.

Although smoked sheet rubber has been selected as illustrative, rubbers in which the products of the present invention are useful include both natural rubber and synthetic rubber. Rubber includes sulfur-vulcanizable diene polymers, preferably those containing a major proportion of diene polymer. Hydrocarbon diene rubbers are preferred but also useful are copolymers of diene hydrocarbons and acrylonitrile. Furthermore, isobutylene copolymerized with a small amount of diene (Butyl rubber) can be used in practice of the invention. Isoprene or butadiene-1,3 copolymers with vinyl monomers copolymerizable therewith, as for example styrene, are illustrative of the preferred diene rubbers. The amount of thiuram sulfide added to the rubber will vary widely depending upon the purpose of the compounder. In general, the amounts will fall within the range of 0.1 to 10 parts by weight per hundred parts by weight of rubber.

The foregoing data show that the compounds of this invention possess stronger accelerating and vulcanizing properties and impart greater processing safety as compared to polymethylene thiuram sulfides heretofore known.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A diene rubber containing a compound of the formula where x is an integer at least 5 but less than 7 and y is an integer at least 1 but less than 5 in an amount effective to accelerate the vulcanization of the rubber at vulcanization temperature.

5. A sulfur-vulcanizable diene rubber according claim 4 where x is 5 and y is 2.

6. A sulfur-vulcanizable diene rubber according claim 4 where x is 6 and y is 2.

7. A sulfur-vulcanizable diene rubber according claim 4 where x is 5 and y is 1.

8. A sulfur-vulcanizable diene rubber according to claim 4 where x is 6 and y is 1.

References Cited UNITED STATES PATENTS 6 FOREIGN PATENTS 415,790 7/1932 Great Britain.

JOSEPH L. SCHOFER, Primary Examiner 5 C. A. HENDERSON, JR., Assistant Examiner US. Cl. X.R. 

